The use of on-site and remote geosteering methods are well known in the downhole drilling arts. During such geosteering operations, drilling typically proceeds according to a predetermined well plan (e.g., derived using geometric considerations in combination with a three dimensional model of the subterranean formations). Real-time geological measurements, for example, measurement while drilling (MWD), logging while drilling (LWD), and/or mud logging measurements, are made while drilling. Data obtained from these measurements are then used to make “on the fly” adjustments to the direction of drilling, for example, to maintain the drill bit at a desired location in a payzone.
In prior art geosteering operations, steering decisions are made at the surface, e.g., at the rig site or at a remote location. LWD data (or other downhole data) are compressed downhole and then transmitted to the surface while drilling (e.g., via conventional telemetry techniques). The transmitted data is then processed at the surface in combination with a model of the subterranean formations to determine a subsequent drilling direction (or a correction to the current drilling direction). Changes to the predetermined (preplanned) drilling direction (e.g., in the form of a corrected well path) are then transmitted from the surface to a downhole steering tool (e.g., via conventional downlinking techniques).
While such geosteering methods are commercially utilized, there remains room for improvement. For example, the viability of prior art geosteering methods is often limited by the bandwidth and accuracy of the communication channel between the bottom hole assembly (BHA) and the surface. This limitation can cause geosteering methods to be slow and somewhat unresponsive (e.g., due to the time lag associated with transmitting LWD measurements to the surface and then transmitting steering instructions or a corrected well plan from the surface to the BHA). Moreover, telemetry errors and/or the reduced accuracy that results from data compression can lead to further errors when computing the corrected well path. These and other limitations of prior art techniques lead to a need for improved geosteering methods.